Catheter-based renal denervation (RD) has been introduced recently as a potentially effective invasive treatment of refractory hypertension. The proportion of patients with severe hypertension suitable for RD is not clear. The aim of this study was to identify what percentage of patients has truly resistant essential hypertension and are thus potentially eligible for RD. We investigated 205 consecutive patients referred to a university hypertension center for severe hypertension within 12 months. Ambulatory 24-h blood pressure (BP) monitoring (24 h ABPM), secondary hypertension screening and compliance to treatment testing (by use of plasma drug level measurements) were performed in all patients. Fifty-seven patients (27.8%) did not have truly resistant hypertension (RH) based on clinical BP. Among the remaining 122 patients (59.5%) with RH confirmed by 24 h ABPM, 50 patients (24.4% of the original cohort) had a secondary cause of hypertension and in 27 (13.2%) non-compliance to treatment was confirmed. Thus, only 45 patients (22%) had truly resistant essential hypertension and were considered for RD. Only one-third (n=15, 7.3% of the original cohort) was, however, finally referred for RD (14 were excluded due to contraindications for RD and 16 refused the invasive treatment). In conclusion, thorough examination of severe hypertension including 24 h ABPM, secondary hypertension exclusion and drug compliance testing before considering RD reveals that majority of these patients are not suitable for RD. Specifically, compliance to treatment testing should be mandatory in order to identify eligible candidates for RD.